Compositions having isocyanate functional components are utilized in a variety of useful products such as adhesives, molded products and foams. Such compositions are utilized in construction, vehicle manufacture, assembly of electronic subassemblies and devices, toys and the like. The adhesives are used to bond substrates together. Such adhesives have found widespread use because they allow for reasonable processing conditions and exhibit good adhesion to many substrates. One common use of such compositions is to bond glass, often in the form of windows, into structures. In automotive assembly plants windows are often bonded in with one part adhesive compositions containing isocyanate functional components. One-part isocyanate functional adhesives typically contain one or more isocyanate functional materials in the form of polyisocyanates or isocyanate functional prepolymers and a catalyst for the cure of the adhesive. Typically, these adhesives cure as a result of exposure to moisture and are protected from moisture until applied to a substrate. One part adhesives are used because the equipment required to dispense and apply the adhesives is less complex than the equipment used to apply two-part adhesive compositions. One part moisture curing adhesives known in the art are disclosed in U.S. Pat. No. 4,374,237, U.S. Pat. No. 4,687,533, U.S. Pat. No. 4,780,520, U.S. Pat. No. 5,063,269, U.S. Pat. No. 5,623,044, U.S. Pat. No. 5,603,798, U.S. Pat. No. 5,852,137, U.S. Pat. No. 5,922,809, U.S. Pat. No. 5,976,305, U.S. Pat. No. 5,852,137 and U.S. Pat. No. 6,512,033, relevant portions incorporated herein by reference. Examples of commercial one part adhesives include BETASEAL™ 15630, 15625, 61355 adhesives available from The Dow Chemical Company, EFBOND™ windshield adhesives available from Eftec, WS 151™, WS212™ adhesives available from Yokohama Rubber Company, and SIKAFLEX™ adhesives available from Sika Corporation.
A two-part polyisocyanate based adhesive comprises, in one part, a polyisocyanate or an isocyanate functional prepolymer and in a second part a curing agent and catalyst for the reaction of the curing agent with isocyanate groups. Typically, the curing agent is a compound having on average more than one active hydrogen atom, for instance an amine or hydroxyl moiety. Two part adhesives are often used for bonding replacement windows into vehicles. Examples of such systems include the adhesive systems disclosed in the commonly owned patent application titled COMPOSITION USEFUL AS AN ADHESIVE FOR INSTALLING VEHICLE WINDOWS filed in the United States on Jun. 3, 2007 having a Ser. No. 11/824,984 and filed in the PCT on Jun. 5, 2007 having a serial number PCT/US07/013; U.S. Pat. No. 6,965,008; EP 1433802 and EP 1578834, all incorporated herein by reference. The adhesive starts to cure when the two parts are contacted. Two-part adhesives have the advantage that they cure much faster than one-part adhesives.
Such products can undergo degradation in properties with use and exposure to natural elements. Exposure to sunlight, humidity and thermal cycling can impact the rate of degradation. To reduce or prevent this from occurring stabilizers are commonly added to the formulations utilized to prepare cured polyurethanes. See for example Wu U.S. Pat. No. 6,512,033 and Zhu et al. United States Patent Application 2006/0270807 paragraphs 0043 to 0046.
Due to market conditions manufacturers of isocyanate based compositions may need to change ingredients utilized in the curable compositions (such as adhesives). Many compositions containing isocyanate functional prepolymers are sensitive systems in that changes in ingredients can alter how the adhesive compositions function or perform (e.g. adhesive systems). Some ingredients such as fillers, plasticizers, thixotropes and the like when changed can impact how curable compositions function and the durability of the compositions. Such changes may result in stabilizer packages becoming ineffective in the altered composition.
Curable compositions that exhibit improved durability are desired. There is a need for compositions (e.g. adhesive) containing isocyanate functional prepolymers which have improved stabilizer packages to replace known stabilization packages which are found not to function properly, especially in compositions where ingredients (such as fillers and/or plasticizers) have been changed. Such compositions exhibit good durability in use and in tests designed to predict long term durability.